1. Field of the Invention
The present invention relates to a battery charging controlling apparatus and battery balance charging controller, and more particularly, to the battery balancing charging controller for balancing battery charging and the battery charging controlling apparatus using the battery balance charging controller.
2. Description of Related Art
With development of portable electronic products, there is a growing need of chargeable batteries. The chargeable batteries include conventional nickel-cadmium battery, later-developed Nickel-hydrogen battery, Lithium (Li) ion battery, and the latest-developed Li-Polymer battery. Different kinds of chargeable batteries may provide different voltages, and operating voltages required by portable electronic products may also be different as well. Therefore, battery manufacturers may make several battery connected in series to form a battery module in accordance with the operating voltages of the portable electronic products.
The battery module is required to be recharged by a charger for use of next time when an electric energy of the battery is exhausted. However, the battery module may have different electric storage capacity due to manufacturing error or using. For example, a Li ion battery module of 7.4 Volts (V) is composed of two Li ion battery of 3.7 V connected in series. At the time of shipment from a factory, the electric storage capacity of the two Li ion battery are 80% and 70% respectively. Due to over-charging the Li ion battery may damage the battery itself, a charger for the Li ion battery terminates charging when any one of the Li ion batteries is fully charged. At this moment, the electric capacity of the two Li ion batteries may be 100% (the upper limit of charging the Li ion battery) and 90%. On the other hand, when the electric capacity of any one of the Li ion batteries is lowered to 0% (the lower limit of discharging the Li ion battery) during operation, the battery module is not usable. As a result, at this moment, the electric capacity of the two are lowered to be 10% and 0%, and the Li ion batteries require to be charged again before the next time of use.
As may be understood from the above-described example, when the electric capacities of batteries of the battery module are different, actual usable electric energy from the battery module may be determined by a battery with a lowest electric capacity. In addition to the above-described example of different electric capacity of each battery of the battery module at the time of shipment, the batteries may discharge by self-discharge when the batteries is not used and the discharging rates of the batteries may be different, such that the electric capacity between the batteries may gradually become unbalanced. It results in the actual usable electric energy of the battery module decreasing along with the utilization of the batteries and then shortening utilization duration of the battery module.
Referring to FIG. 1, this is a digital battery balance controller disclosed in a datasheet of the Intersil ISL9208. A digital battery balance controller 10 include a battery balance microprocessor 5 and transistor switches S1˜S7. The transistor switches S1˜S7 are respectively connected in parallel with batteries BAT1˜BAT7 via resistors R1˜R7. Voltage levels of the batteries BAT1˜BAT7 are converted via an analog/digital converter (A/D converter) to digital signals. Then, the battery balance controller microcontroller 5 determines which battery has a higher voltage by executing a built-in algorithm based on the digital signals indicative of the voltage levels of the batteries BAT1˜BAT7, and thus conducts the transistor switch connected in parallel with the battery of the higher voltage. Therefore, charging current of each battery can be adjusted according to the voltage of each of the batteries so as to achieve functionality of balancing charging.
However, the battery voltages are required to be transformed to digital signals via the A/D converter for the digital battery balance microcontroller 5 processing. The A/D converter may substantially increase chip area of the digital battery balance controller 10, and so relatively high cost is a disadvantage to this approach. In addition, the digital battery balance microcontroller 5 may be limited to original design, for example, ISL9208 may only support a battery module with 5 to 7 batteries, application scope of the digital battery balance controller may be limited as a result.